Equipment exists that is designed to be carried by people and that comprises an electrical appliance equipped with a battery. Unfortunately, in order to have a sufficient reserve of energy, the battery is relatively heavy and voluminous, making the equipment uncomfortable and tiring to carry, in particular when the user has to carry it for a long time or has to make efforts while carrying it.
In order to obviate that drawback, it has been imagined to power the electrical appliance by means of a separate power supply circuit having two batteries. The use of two batteries that are separate from the appliance is advantageous because the batteries and the appliance can be disposed at different places on the body of the user. The weight of the equipment is then distributed over the user, making it more comfortable and less tiring to carry the equipment.
Such a power supply circuit includes a first battery and a second battery that are connected to a connection member that is external to the circuit via a switch device that is suitable for being actuated to go into a first connection state and into a second connection state, in which states it connects respectively the first battery or the second battery to the external connection member. The circuit also includes a management member that is arranged to detect a level of charge in each of the batteries and that is connected to the switch device for causing the switch device to go over from the first connection state to the second connection state when the first battery has a level of charge that is less than a predetermined threshold. Thus, the battery that is discharged to the greatest extent is used so long as its level of charge is sufficient to power the equipment. A user of the appliance having access to a stock of recharged batteries need only change one battery if the switch has remained in its first connection state whereas if both of the two batteries were used without distinguishing between them, the user would have had to change both batteries in order to have a maximum reserve of energy. That simplifies managing the stock of recharged batteries, and makes it possible to reduce the size of said stock compared with the stock that would be necessary if the user always changed both batteries.
Nevertheless, the length of operating time procured by the batteries before they need to be recharged remains insufficient for using the equipment for long periods, in particular in cold weather when the batteries have high internal resistance that reduces their performance.